This study was an attempt to find out whether co-teaching model has statistically any significant impact on improving motivation and achievement of Iranian Young EFL Learners or not. The study was conducted at Salehin English Language Department in Tehran. To accomplish the purpose of this study, the researchers chose a sample of 91 participants which was reduced to 62 homogenous students through administration of YLE test. Then, these participants were divided randomly into two 30 and 32 participants groups as experimental and control groups. The participants in both experimental and control groups, were tested on test and questionnaire as pretests in the first session. In the following 10 sessions, the participants in the experimental group received co-teaching lessons, while the control group received traditional teaching. At the end of the term, the same test and questionnaire were administered to the participants of both groups as the posttests to check the effectiveness of the treatment. Finally, the means of both groups were compared through t-test (α=.05). The results indicated there were significant differences between the performances of both groups. It was concluded that participants who received teaching by two teachers, outperformed those who did not.